Antisera prepared against BALB/c Meth A sarcoma in syngeneic or compatible F1 mice recognize a protein with an apparent molecular weight of 53,000 in extracts of [35S]methionine-labeled transformed BALB/c cells. This component, designated p53, was not detected in normal adult mouse fibroblasts, lymphoid cells, or hematopoietic cells or in mouse embryo cells or 3T3 cells. An extensive variety of antisera, including alloantisera and heterologous antisera directed against structural antigens of murine leukemia viruses, was tested for reactivity with p53; other than Meth A antisera, only comparably prepared antisera against another BALB/c sarcoma, CMS4, had anti-p53 activity. All transformed mouse cells tested were found to express p53; these tests included chemically induced sarcomas, leukemias, spontaneously transformed fibroblasts, and cells transformed by simian virus 40 and murine sarcoma virus. The presence of p53 in tumors of no known viral etiology indicates coding by resident cellular genes; this does not exclude endogenous viruses as the source of coding sequences or the possibility that transforming viruses code directly for p53.

A tumor-specific transplantation antigen has been purified to homogeneity from the cytosol of a methylcho- We now report on the purification to homogeneity and the biochemical characterization ofa cytosolic TSTA, from Meth A, that consists of two polypeptide isoforms of similar size and charge. Sequence analysis of the two isoforms indicates that a large portion of the sequenced NH2-terminal region of both proteins, as well as a CNBr fragment, shares extensive sequence homology with the Drosophila melanogaster 83-kDa (7) and yeast 90-kDa heat shock protein (8).Upon stress, cells from bacteria to mammals decrease the synthesis of most proteins but transiently increase the synthesis of several heat shock, or stress, proteins (9, 10). One of the major heat shock proteins is an acidic cytosolic protein whose apparent molecular mass in the mouse is [85][86][87][88][89][90]12 MATERIALS AND METHODSPurification of TSTA. The Meth A TSTA was purified from 2.5 x 1010 Meth A ascites cells as described (3, 4) except for an additional step. The hydroxyapatite-purified antigen was equilibrated with 20 mM Tris Cl (pH 8.0) in 10% (wt/vol) glycerol (buffer A) and then injected into a Mono Q HR5/5 column (Pharmacia) equilibrated with buffer A. The antigen was eluted with a 0.3-0.6 M gradient of NaCl in buffer A. Purity of TSTA was determined by two-dimensional PAGE, and TSTA activity was measured as described (3 3121The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

The synthetic double-stranded RNA, polyinosinic-cytidylic acid, inhibits the growth of some tumors in mice. Two days after implantation of a reticulum cell sarcoma, a lymphatic lymphoma, a fibrosarcoma, two leukemias, and a human adenovirus 12-induced tumor, treatment of groups of mice resulted in decreased growth rates of the tumors and increased survival times of the animals. In the two tumors tested (the reticulum cell sarcoma and the adenovirus 12-induced tumor) initiation of treatment after the tumor was grown to moderate size caused a regression of the tumor. In the case of the reticulum cell sarcoma, the tumor had not reappeared in some of the animals two months after cessation of treatment.

Four assays of tumor-specific cell-mediated immunity were compared during growth of a syngeneic Simian-virus-40-induced tumor, mKSA. Major differences were found in immunity detected by the tumor neutralization test (the Winn test), direct tumor challenge, the microcytotoxicity assay and the -51chromium-release lymphocytotoxicity assay. Progressive growth of the neoplasm followed by loss of immunity (the eclipse phenomenon) was documented with the Winn test. It was established that this eclipse phenomenon represented a lesion in the T-cell system of tumor-bearing hosts. This lesion was found to be specific and unrelated to anatomic tumor location. The ability to produce graft-versus-host reactions, and the ability to respond to mitogens, were found to be generally intact in tumor-bearing animals. Cells capable of recognizing mKSA tumor antigens and reconstituting an immune response following surgical removal of tumor or upon transfer to normal mice were found in the spleens of mice bearing advanced tumors. No suppressor cells that might account for the eclipse phenomenon could be demonstrated. Tumor-bearer serum did not block neutralizing activity of immune spleen cells in the Winn test, and immune cells were capable of neutralizing tumor even in tumor-bearing hosts. The possibility that the lesion is intrinsic to T-cell precursors of effector cells is discussed.